Freeman A J, Gowland P A, Mansfield P
Magnetic Resonance Centre, Department of Physics, University of Nottingham, UK.
Magn Reson Imaging. 1998 Sep;16(7):765-72. doi: 10.1016/s0730-725x(98)00011-3.
The Look-Locker echo-planar imaging (LL-EPI) sequence has been numerically optimized in terms of the signal-to-noise ratio in the measured value of T1, for both single-shot (repetition time (TR) = infinity), and dynamically repeated T1 measurements. The sequence is optimized for the normal biologic range of T1 (0.2 s to 2.0 s) and for a range of sequence parameters found on most magnetic resonance (MR) scanners. Both linearly and geometrically spaced magnetization sample pulse intervals were considered. For single-shot measurements, the sequence with 24 linearly spaced sample pulses, an inversion time of 0.01 s, an inter-sample pulse delay of 0.10 s, and a sample radiofrequency (RF) pulse flip angle of 25 degrees was found to be optimum. When the number of sample pulses was limited due to hardware limitations, different pulse sequence parameters were indicated. The optimization procedures used are appropriate for any single-shot T1 mapping sequence variant and for any rapid T1 mapping application. The use of an optimized Look-Locker echo-planar imaging sequence is demonstrated by an example of dynamic contrast-enhanced scanning in the brain using fast T1 mapping.
Look-Locker回波平面成像（LL-EPI）序列已针对单次激发（重复时间（TR）=无穷大）和动态重复T1测量的T1测量值中的信噪比进行了数值优化。该序列针对T1的正常生物学范围（0.2秒至2.0秒）以及大多数磁共振（MR）扫描仪上发现的一系列序列参数进行了优化。考虑了线性和几何间隔的磁化采样脉冲间隔。对于单次激发测量，发现具有24个线性间隔采样脉冲、反转时间为0.01秒、采样脉冲间延迟为0.10秒以及采样射频（RF）脉冲翻转角为25度的序列是最佳的。当由于硬件限制采样脉冲数量有限时，指出了不同的脉冲序列参数。所使用的优化程序适用于任何单次激发T1映射序列变体和任何快速T1映射应用。通过使用快速T1映射在脑部进行动态对比增强扫描的示例展示了优化的Look-Locker回波平面成像序列的应用。
